Dippy, I just thought that I should flag up what a helpful few paragraphs of guidance that is; explanatory, pragmatic, appropriate and realistic. That is precisely the type of advice and information that makes you such a valued contributor to this forum and makes the forum so worthwhile reading - for everyone whatever their level of experience. Just a note of appreciation for the time that you put in with your (now over 10 000!) pieces of good counsel.
5vdc power supply
- Thread starter jims
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You're very kind, though I wish I had re-read it before pressing the tit.
(Not ALL 10,000 were good counsel though
)
I also wish that the once-up-a-time (4 years ago?) suggested 'Tutorial' section had been created.
Then we could have had a place for things like this, with better explanations, diagrams and some calcs.
We have 'Code Snippets', so why not 'Circuit Snippets' and 'Tips and Tricks' like (for example) the Proton Forum (other Forums are available).
(Not ALL 10,000 were good counsel though
)I also wish that the once-up-a-time (4 years ago?) suggested 'Tutorial' section had been created.
Then we could have had a place for things like this, with better explanations, diagrams and some calcs.
We have 'Code Snippets', so why not 'Circuit Snippets' and 'Tips and Tricks' like (for example) the Proton Forum (other Forums are available).
Of course. This discussion is about *where* those reservoirs belong (based on the earlier article).
And the best place to put the 'reservoir' is as close to the relay/IRLED as you can get it, not some random location between the device and the regulator.
And there are ways to calculate the size of a capacitor to support the need of a given device. But the problem is the recommendation to put reservoirs 'somewhere convenient' along the line. How do you calculate the required value of a capacitor that is two inches from the regulator and three inches from the device that needs the reservoir? And if you've provided for the regulator at the regulator and provided for the device at the device, why put something random in between? That is the practise that was not mentioned in the article and yet is done so frequently.
Is that a serious question or sarcasm?
Exactly! That is what I'm saying. And it should not be at some random point along the way.
Again, exactly! And potentially lethal to the circuit if the amount of capacitance exceeds the regulator's ability to handle short circuits or turn-off pulses because there are no protection diodes in the circuit.An engineer from TI wrote an excellent and amusing article about the habit of novices "throwing" capacitors at circuits without proper consideration (I've done it myself before). You often don't need to chuck a zillion microfarads randomly into a circuit. And sometimes it can be harmful.
I have to add this is where simulators can help the grey matter
Yes, to all of that. But if best practise is to provide capacitance at the regulator for stability and the rest of the capacitance as close as possible to the device causing the abrupt demand changes, why recommend unspecified (and uncalculable) amounts of capacitance at some random point in the circuit between the regulator and the device drawing current?Summary.
No, 'reservoir capacitors' are here to stay where needed.
You, as the designer, need to work out the best position and value.
Though, quite often, guesswork and a little over-engineering works just fine
And there is always the issue of accidentally exceeding the manufacturer-specified maximum capacitance on the output of the regulator which leaves the circuit susceptible to regulator failure due to backflow of current in some circumstances.
Several people have defended the practise of random reservoirs between supply and device but always using the example of a device suddenly shifting current demand, and this is exactly the situation that demands capacitance local to the device, not some distance down the line. There seems to be no reason to put capacitance in the circuit in locations other than at the regulator and at the devices drawing current, and only in the correct amount.
We've all done it -- capacitance in the line somewhere 'just because' but maybe with consideration we might change our pracises to putting the correct amount of capacitance exactly where it belongs?
Blimey!
I was giving a simple example/answer to paragraphs 2 and 3 of your post #39.
You appeared to be questioning the need for a resrvoir in para 2.
And , in para 3, you asked how you calculate the size and position - which, to me, suggested you were asking a question.
And now you seem to be answering your own questions...
No I wasn't being sarcastic, though I had a bet (with myself) that it might be thought as such.
Knowing loads/times/energies/time-constants/impedances and equating that with requirements is part of the basics of the reservoir calculation. It wasn't clear in your previous post whether that was appreciated, so it was a serious question.
I've never been an advocate of slapping capacitors any-old-where.
But I'm not going to dismiss that in some circuit layouts in some circumstances that capacitors may need to be placed in other places. And sometimes it would be asking for trouble. For example, it's unlikely you'd do it after an output of an op-amp for reasons that are obvious.
Wap you've got to understand that I work (design and assessment) in electronics in C&I, power and communications. It's full of maths and calculus and physics and it's sometimes a little tricky for me to know other people's experience and qualifications.
Anyway, I'm done with this one. Life is too short.
I was giving a simple example/answer to paragraphs 2 and 3 of your post #39.
You appeared to be questioning the need for a resrvoir in para 2.
And , in para 3, you asked how you calculate the size and position - which, to me, suggested you were asking a question.
And now you seem to be answering your own questions...
No I wasn't being sarcastic, though I had a bet (with myself) that it might be thought as such.
Knowing loads/times/energies/time-constants/impedances and equating that with requirements is part of the basics of the reservoir calculation. It wasn't clear in your previous post whether that was appreciated, so it was a serious question.
I've never been an advocate of slapping capacitors any-old-where.
But I'm not going to dismiss that in some circuit layouts in some circumstances that capacitors may need to be placed in other places. And sometimes it would be asking for trouble. For example, it's unlikely you'd do it after an output of an op-amp for reasons that are obvious.
Wap you've got to understand that I work (design and assessment) in electronics in C&I, power and communications. It's full of maths and calculus and physics and it's sometimes a little tricky for me to know other people's experience and qualifications.
Anyway, I'm done with this one. Life is too short.
Yeah, me too.